Existing infrared spectra from high speed interferometer balloon flights were analyzed and experimental analysis techniques applicable to similar data from the ATMOS experiment (Spacelab 3) were investigated. Specific techniques under investigation included line-by-line simulation of the spectra to aid in the identification of absorbing gases, simultaneous retrieval of pressure and temperature profiles using carefully chosen pairs of CO2 absorption lines, and the use of these pressures and temperatures in the retrieval of gas concentration profiles for many absorbing species. A search for a new absorption features was also carried out, and special attention was given to identification of absorbing gases in spectral bandpass regions to be measured by the halogen occultation experiment

Park, J. H.

Russell, J. M., III

Smith, M. A. H.

Twitty, J. T.

English

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{	
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(NASA-TM-80465) ATMOS SPACELAB 1 SCIENCE	 N79-24568
INVESTIGATION Final Report, 1 May 1976 - 30
Apr. 1979 (NASA) 19 p HC A02/MP A01
CSCL 04A	 Unclas
G3/46 22169
The College of William and Mary
Williamsburg, Virginia 23185
Final Report
May 1, 1978 - April 30, 1979
NASA Grant NSG 1484
ATMOS Spacelab I Science Investigation
Mary Ann H. Smith
Research Associate
Jae H. Park
Research Assistant Professor
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Research Summary
Research Title: ATMOS SPACELAR I SC 1110E INVESTIGATION
Research Period: May 1, 1978-April 30, 1979
Grant Number, NSG-1484
Investigators:	 PI: Dr. Jae H. Park, College of William and Mary,
Williamsburg, Virginia 23185 (804)827-2576
CO-I: Dr. Mary Ann H. Smith, College of William and Mary,
Williamsburg, Virginia 23185 (804)827-2576
CO-I: Dr. Jerold T. Twitty, Systems and Applied Services
Corporation, Riverdale, Maryland 20840
(804)827-25'76
CO•I: Dr. James 14. Russell III, NASA Langley Research
Center, Hampton, Virginia 23665 (804)827-2576
Description of Fesearch and Results:
i
Analysis of existing infrared spectra from JPL's Mark I High Speed
Interferometer (HSI) balloon flights (1976, 1977) and development of analysis
techniques applicable to similar data from HSI Mark II balloon flights (1979)
and from the ATMOS experiment (^Dacela} III). Specific techniques under
development include line-by-line simulation of the spectra to aid in the
identification of absorbing gases, simultaneous retrieval of pressure and
temperature profiles using carefully chosen pairs of CO 2 .absorption lines,
and the use of these pressures and temperatures in the retrieval of gas con-
centration profiles for many absorbing species. A search for new absorption
features was also carried out, and special attention was given to identification
of absorbing gases in :.,ectral bandpass regions to be measured by the Halogen
Occultation Experiment (HALOE).
Future Plans:
The temperature and pressure inversion and gas concentration inversion
algorithms will be further developed and refined, and will be used to retrieve
profiles from the Mark I data and from the Mark II data to become available
in late 1979. The search for new absorption signatures in the Mark I and Mark
II spectra wi'.l continue, leading to the determination of actual amounts or
upper limits f)r the stratospheric concentrations of CH 3C£, Cif 3CCE39 If2CO and
OCS. More efficient techniques for line-by-line simulation of t:ie spectra will
also be explored.
:S
II. Investigations
1. Identification of Major Absorbers
2. Simulation of the Spectra
3. Pressure and Temperature Sensing Using, CO 2
 Lines
i+. Simultruieous Retrieval of Gas Concentrations
5. Support for HALOE
6. Line Identification and :search for New ^ignatures
III. Sumrmiary
TV. References
V. List of Figures
I-
6
I. INTRODUCTION
:tie primary purpose of the proposed research has been to analyze
existing high-resolution infrared spectra measured by JPL's Mark I High Speed
Interferometer (HSI) in balloon-borne solar occultation experiments (1976 and
1977), and to develop analysis techniques applicable to similar data from the
Mark II instrw.lent to be flown on a balloon in mid-1979 and data from ATMOS,
which is now scheduled to fly on Spacelab III (1982). -The specific objectives
of the current study include identification of major absorbers in the Mark I
spectra, simulation of the absorption spectra using a line-by-line method for
comparison to the measured spectra, development of inversion techniques to
obtain pressure and temperature profiles from CO 2 absorption lines, and the
use of these pressures and temperatures in the simultaneous retrieval of various
gas concentrations, focusing primarily on the rases and spectral regions impor-
tant for HALOE (Haloren Occultation Experiment). Unknown features in the existing;
spectra were also to be identified and studied in more detail, with specific
attention being given to the spectral region of the v 4 band of CH 3Ck. In the
following pages of this report, the above-mentioned objectives will be dis-
cussed individually, describing both the current status of the research and
the work planned for the future in each of these areas.
:d
	 1
i
e
II. TNVFSTIGATIONS
I. Identification of Mnjor Absorbers
Selected wavelength regions of HSI Mark I spectra from two different
balloon flights (Texas, 1976 and Australia, 1977) are available in graphical form, and
the complete spectra :ire stored In digital form on ma t*netle tape. With the help of
the Atlas of Infrared Absorption Lines (NUM CR-2925) published at NAOA Langley Re-
-eareh Center, as well as additional data on methane (CH 4) provided by Dr. 'loth at
JPL, features belonging to the major absorbing gases (H 2O, CO2 , 03, C114, N20)
are readily identified in the graphical spectra. A spectral plotting program,
:erived from one developed by R. Norton ;w d B. Stedry at JPL, allows the
display of spectral data with a scale and resolution chosen by the user
(Fig. 1). Coupled with the line-parameter plotting progr:uu used to generate
the Atlas (Fig. 2), the spectral plotting program facilitates the identifica-
tion of a large number of absorption features in the Mark I spectra.
Simulation of the :Ipcetra
A multi-gas version of the line-by-line model developed by Drayson
(1966) has been used to simulate several regions of the HSI Mark I spectra
(Fig. 3). The model has been modified to include the effects of the real
instrumental line shape for the interferometer, :uid a faster routine to
calculate the Voigt line shape (Drayson, 1976) has been included. Parameters
in the model can be easily changed in order to simulate the hit-h-resolution
Mark II spectra when they become available. The agreement between the simu-
lated spectra and the measured spectra is quite Food. The remaining discrep-
ancies are almost entirely due tothe amounts of gases assumed in the model,
F
3filter effects present in the measured spectra, and, in some spectral regions,
missing or uncertain line parameters input into the model. The computational
efficiency and speed of the model, running on the CDC 6600 computer, have been
improved, but the total cost of the simultations remains high. An alternative
and more efficient simulation technique, based on the Fourier-Transform method
of Dr. Mankin at NCAR, which runs on the STAR computer at LaRC, has been
successfully used in LIMS data analysis at this center. This FFT model will
be tested and evaluated for use in simulating HSI and ATMOS spectra.
'. Pressure and Temperature Sensing Using CO., Lines
In order to obtain gas concentration profiles in a limb-viewing
experiment, it is desirable to get temperature and pressure profiles directly
from spectral data rather than relying on climatological data and tangent
heights calculated from instrument pointing information. We have begun develop-
ing an iterative technique for simultaneous retrieval of pressure and tempera-
ture profiles using; a pair of CO2
 absorption lines having different lower-
state energies, but appearing in the same spectrum. Investigation of the
temperature and pressure dependence of CO 2 line strengths has indicated that
lines !iaving, lower-state energies on the order of 0 -800 cm -1 are best suited
for pressure-sensing, while those with lower-state energies greater than
1000 cm " are most strongly temperature-dependent. A technique for temperature
sensing using isolated CO2 lines in the HSI spectra has already been developed
i	 by Toth (1977), and pressures may be retrieves using; a curve-of-growtr method
f	
(Park et al 1979), provided that equivalent widths of the individual CO 2 lines
f	 or a group of lines can be determined with sufficient accuracy. A numerical
algorithm where the retrieved temperature and pressure profiles are used to
correct each other in successive iterations has recently been written and has
1	 been tec ed using- simulated equivalent width values.
4Figures 4 and 5 show the expected error in temperature and pressure for
a single atmospheric layer.. retrieved us,nq the above-mentioned algorithm. As
predicted from analysis of line-strent-th temperature and pressure dependence, the
highest accuracies in retrieved temperatures are achieved for CO 2 lines having lower-
state energies greater than 1000 cm-1 . For the case shown in Fig. 5 where we assume
that the temperature profile is known perfectly (AT = 0), the error in retrieved
pressure does not appear to vary with the lower-state enerpW of the CO 2
 line chosen
for lressure sensing. When uncertainty AT is included in the temperature profile,
the pressure uncertainty Ap remains small for CO 2
 lines having lower-suite energies
less than 600 cm-l . Accuracies for both pressure and temperature retrievals
deteriorate when the absorption line is very weak (absorption less than 10%) or
nearly saturated (absorption greater than 95%). The error analyses in Figs. 4 and
5 were carried out for a rather low atmospheric pressure, 0.7 mb, which corresponds
to an altitude of 50 km. We have found that the accuracy of both the pressure and
temperature retrievals for higher atmospheric pressures is considerably better than
the results shown in the figures.
Testing, and further development of the pressure and temperature retrieval
algorithm will continue, making use of equivalent widths of CO 2
 lines measured in
the HSI Mark I spectra. There is also under development a program which will auto-
matically scan the HSI spectra stored on magnetic tape, find the centers of spectral
lines and calculate their equivalent widths. The line-finding- and equivalent width
routines are based on the DFRPTH program written by H. Delouis at the Centre National
de la Recherche Scientifique, Orsay. Eventually these routines will be incorporated,
^Llong with the atlas and spectral ratio and plotting programs, into a software
iibra.ry for analysis of HSI and AT140S data at LaRC.
4. Simultaneous Retrieval of Ga s Concentrations
Several methods for retrieval of gas concentrations hav, been studied,
among them the direct curve-of-growth method, which requires accurate determi-
nation of equivalent widths, iterative simulation and fitting of line profiles,
5and the equivalent -width-ratio method used by Farmer and Rgper (1977)• An
algorithm for inversion of a gas concentration profile using the single-line
curve of growth method combined with Drayson's to
	peeling" technique has
been written and is currently being tested. Further development and testing
t-f gas-concentration retrieval methods will proceed in parallel with the work
on the temperature and pressure retrievals and automatic calculation of equi-
valent widths. In addition, selection of absorption lines that can be used
for most accurate retrieval of concentrations of stratospheric minor gases will
be carried out.
F	 5. Support for HALOE
Work done as part of Cie current investigation has contributed to
the support of HALOE, aiding in identification of the best spectral regions
in which to detect each of the oases of interest (HICZ, HF, CH 4 , NO, H2O, and
CO2 ). Detailed analysis and line identification in each of the chosen spectral
regions remains to be done, particularly in regard to the identification of
solar lines. Line-by-line simulations have already been carried out for each
of these regions, and the pressure, temperature and gas concentration retrieval
algorithms under development in this investigation will be applied first to
the HALOE spectral regions. The gas concentration profiles determined from
the HSI spectra will be used to refine previous sensitivity analyses for HALOE.
Retrieval of HCQ mixing;-ratio profiles will receive high priority because the
HALOE brass poard instrument for the HCk channel will be test-flown on the CV990
in the summer of 1979• Since both the ATMOS and HALOE instruments are now
scheduled to fly on Spacelab III, there will be a unique opportunity for com-
parison of gas concentration profiles determined from the two experiments.
0(
AMON
66. Line Identification and --arch for New Signatures
An extensive analysis and search for new signatures has been carried
out for the spectral region between 3055 and 3075 cm -1 .
	Attention
was focused on this region to determine if absorption features belonging to
the v4
 fundamental of methyl chloride (CH 3CO were detectable in the HSI Mark I
spectra. By comparison of the real spectra with Atlas line data and simulated
spectra, there was found a broad, weak absorption feature extending between
3062 and 3072 cm 1, which appears in the Texas spectra but not in the Australian
data. Several species including H 2O, CO2 , 03 and CH  have been ruled out as
the cause of this feature. Simulations of CH 3C2 absorption in this region,
assuming its stratospheric mixing ratios to be one to ten times the values
calculated by Crutzen et al 	 (1978), seem to indicate that methyl chloride
alone could not account for the broad envelope found in the Texas spectra.
The Sum absorption spectra of other halogenated hydrocarbons, including methyl
chloroform (CH 3CCR 3 ), are now being studied and compared to the Mark I data
in an effort to make a definite identification of the broad feature. Upper
limits on the stratospheric concentrations of' CH 3CZ, CH 3CCQ3 and other halo-
genated hydrocarbons will be calculated after the identification of the
broad feature is made.
Preliminary surveys of the Mark I spectra to search for the signa-
tures of Freon-14 (CF 4), formaldehyde (H2CO) and carbon„•1 sulfide (OCS) have
also been carried out. Since the stronr, v 3
 and v4
 absorption bands of CF  lie
outside the bandpass of the filters used in the Mark I balloon flights, we
cannot determine anything about CF  concentrations from this data. Formaldehyde
and carbonyl sulfide have strong absorption bands at 3.511n and Sum (see Fig. 1),
f
L
7respectively, which have not been detected in the Mark I spectra through
visual inspection. However, careful analysis of the spectra in these regions
and simulations of the spectra based on accurate laboratory data may reveal
weak absorption by OCS or H2CO in there two regions and allow the determinrt--
Lion of gas concentrations or upper limits for these stratospheric trace
species.
i
bLi
8TIT. ''MARY
Considerable F. ••gress has been made this year in a number of the
research areas specified in the objectives of this study. Identification of
absorption features belonging to major infrared-active atmospheric constituents
in any region of the :dark I spectra is accomplished readily by the use of both
the Atlas and spectral plotting programs. The line-by-line simulation model operat-
ing on the CDC 6600 computer has been made no efficient as possible, and the less
costly FFT model running on the STAR computer may be used for simulation of
HSI data in the near future. Algorithms for the combined retrieval of pressure
and temperature profiles using CO2
 lines and for the retrieval of gas concen-
trations have been outlined, and early versions of numerical routines for these
retrievals have been tested. A new absorption feature in the 3.3um region
has been found in the Texas data, but Is not yet identified. Preliminary
surveys of the spectra have also been carried out in preparation for the
determination of upper limits on the stratospheric concentrations of CH3Ck,
CH 3CU 39
 H 2CO and OCS. The wort, on pressure, temperature and gas concentra-
tion retrievals will be emphasized in the coming year, in support of HALOE
fl if, ht experiments.
11
`r
I
9REFERIIJCES
1. Drayson,	 R., Appl. Optics, 5, 385 (1966).
2. Drayson, :. R., J. Quart. Spect. Rad. Tr., 16, 611 (1976).
3. Farmer, C. B. and Raper, 0. F., Geophys. Res. Lett., 4, 527 (19'7).
4. Park, J. H., Russell, J. M. III and DrVson, S. R., Applied Optic:,
June 15 Issue (1979).
5. Toth, R. A., Appl. Optics, 16, 2661 (1977).
6. Crutzen,P.J., Isaksen,I.S.,and McAfee, J.R., J.Geophys.Res.,83.345 (1978).
!	 i
10
LIST OF FIGURES
Figure 1.
	 Plot of a portion of three spectra from the May 1976 HSI Mark I
balloon flight from Palestine, Texas. The runs '_004, 2000 and
1984 refer to mean tangent heights of 23 km, 33 km, and in excess
of 40 km, respectively.
Figure 2.	 Atlas plot of line data used in the simulation shown in Fig. 3.
Figure 3.
	
Simulation of Run 2004 for the same spectral interval as in the
previous figure.
Figure 4.	 Expected error AT for temperature retrieved for a single layer
using one CO2
 absorption line, assuming that pressure profile is
known exactly (Ap - 0). E" is the lower-state energy of the line
in cm"
Fig+re 5.	 Expected error Ap for pressure retrieved for a single layer
using one CO2 absorption line, assuming that the temperature
profile is known exactly (AT :. 0).
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